void sort(int a[],int first, int last){
    int pivot, i, j, tmp;
    if (first<last){
	pivot = first;
	i = first;
	j = last;
	while(i<j){
	    while(a[i]<=a[pivot]&&i<last)
		i++;
	    while(a[j]>a[pivot])
		j--;
	    if(i<j){
		temp=a[i];
		a[i] = a[j];
		a[j] = temp;
	    }
       }
   temp = a[pivot];
   a[pivot] = a[j];
   a[j] = temp;
   sort(a,first,j-1);
   sort(a,j+1,last);
}
}